Scientists warn on climatic 'tipping points'

An international team of scientists has presented its list of those regions of the planet most at risk from global warming, which are in danger of "sudden and catastrophic collapse" should they pass "tipping point" thresholds beyond which they will never recover.

The researchers, comprising experts from the Potsdam Institute for Climate Impact Research in Germany, the University of East Anglia and Oxford University's Environmental Change Institute, quizzed "52 environmental experts and combined their responses with discussions among 36 leading climate researchers at a workshop at the British embassy in Berlin", the Guardian explains.

UN predictions suggest that global temperatures will rise by up to 6.4°C by the end of the century, with 4°C being a likely figure. This represents very bad news indeed for Arctic sea ice and the Greenland ice sheet, which the team identfied as being top of the chop list.

Specifically, if temperatures rise between 0.5°C to 2°C "above those at the beginning of the century", Arctic sea ice will go into "irreversible decline" - a process which may already have begun.

The Greenland ice sheet, meanwhile, is currently threatened by a 50 per cent possibility that it has already begun terminal meltdown. Although the process could last centuries, the end result would be a seven-metre rise in sea levels globally.

Next up of the environmental apocalypse list is the Amazon rainforest, where "reduced rainfall threatens to claim large areas of trees that will not re-establish themselves". A temperature rise of 3°C to 5°C might reduce rainfall in the Amazon by 30 per cent, extending the dry season, and provoking a vicious circle of decline.

Other threatened ecosystems include northern Boreal forests, "with large swathes dying off over the next 50 years", and the western Antarctic ice sheet, where evidence demonstrates "the balance of snowfall and melting has shifted and it is now shrinking". A local rise in temperature of over 5°C could trigger "uncontrollable melting, adding five metres to sea levels within 300 years".

And just to really cheer us all up, the scientists also predict the collapse of the west African monsoon, increasingly erratic Indian summer monsoons and an intensification of the El Niño climate system which has "a profound impact on weather from Africa to North America".

In summary, the Guardian notes that the predicted 4°C rise in temperatures would cause "droughts and floods, as rainfall increases at high latitudes and drops in the tropics". Africa would be worst affected by drought, suffering a 15 to 35 per cent drop in harvest yields, compared to a global average fall of ten per cent.

Twenty to 50 per cent of land species would meanwhile be driven to extinction, while humanity tackled an estimated 59cm rise in sea levels, threatening low-lying coastal cities.

The team's cheerful findings are published in the Proceedings of the National Academy of Sciences. Lead author Tim Lenton, an environmental scientist of the University of East Anglia, concluded: "There's a perception that global warming is something that will happen smoothly into the future, but some of these ecosystems go into an abrupt decline when warming reaches a certain threshold.

"If we know when the different tipping points are, we can use them to inform targets to limit global warming. It gives us something to aim for." ®

And the good news?

Our own team of experts has calculated that a 4°C rise in temperatures would reduce the need for UK pub patio heaters - deployed in winter to allow nicotine addicts to light up without risking frostbite - by around 46 per cent.

This would result in a 0.0001 per cent reduction in greenhouse gas emissions, and a saving of around 1.4m tonnes of the paper which would otherwise be required by the EU to draft reports on why patio heaters should be banned.